1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to cases, such as molded cases, for electrical switching apparatus. The invention also relates to terminal shields for electrical switching apparatus.
2. Background Information
Electrical equipment such as, for example, relays, circuit breakers, electric meters and transformers, are typically housed within an electrical enclosure such as, for example, a housing such as a cabinet.
Panelboards or load centers, for example, are types of electrical enclosures which serve to distribute power for residential or commercial applications. Typically, the panelboard or load center includes a housing enclosing a plurality of electrical switching apparatus (e.g., without limitation, circuit breakers) for protecting branch circuits against electrical faults or overload conditions. It is desirable to maximize the efficiency with which the available space within the housing is used. Accordingly, the circuit breakers are often disposed, for example, adjacent one another in parallel rows with one or more bus bars extending between the rows. The circuit breakers may also be removably coupled to a DIN rail. DIN is short for Deutsches Insitut für Normung eV, which is a German standard-setting organization. Accordingly, a DIN rail is a connecting rail structure which is designed to satisfy DIN standards. Some manufacturers of circuit breakers provide the circuit breaker with a DIN rail mounting structure, such as an integrally molded recess sized to provide snap-on attachment to the DIN rail.
FIG. 1 shows an example of three such circuit breakers 2, which are ganged (e.g., coupled) together side-by-side. Each circuit breaker 2 is essentially identical, including a case 6 with a first half 8 and a second half 10. Handles 12 protrude from the top (from the perspective of FIG. 1) of the cases 6 and, in the example of FIG. 1, are ganged (e.g., coupled) together. The end 4 of each circuit breaker 2 includes a terminal 14, with protrusions 16,18 being disposed on opposite sides of the terminals 14. A single vent 20 provides the sole means for ventilating ionized gases from within each circuit breaker 2. The interior of the second half 10 of one of the circuit breakers 2, and the terminal 14, protrusion 18 and vent 20 thereof are shown in FIG. 2, which also shows the aforementioned molded DIN rail mounting structure 22.
Circuit breakers (e.g., circuit breaker 2) are subject to industry safety regulations. For example and without limitation, the Underwriter's Laboratory (UL) establishes minimum spacing requirements between the terminals of adjacent circuit breakers. Specifically, there is both a “through air” minimum spacing requirement, and an “over surface” minimum spacing requirement. “Through air” refers to the shortest direct path over which an arc could potentially jump, through the air, for example between respective terminals 14 of any two of the adjacent circuit breakers 2. “Over surface” refers to the shortest path between, for example, adjacent terminals 14 wherein such path is over the surface of a portion or portions (e.g., protrusions 16,18) of the respective circuit breaker casings 6 of the adjacent circuit breakers 2.
It will be appreciated that it is difficult to satisfy such regulations while simultaneously meeting the design goal of minimizing the space required for the circuit breakers, and thus the overall space required for the corresponding electrical enclosure. It is, therefore, desirable to space circuit breakers as closely together as possible while satisfying industry safety standards such as, for example, minimum terminal spacing requirements.
There is, therefore, room for improvement in electrical switching apparatus and in cases therefor.